In 2025, Dutch Customs' radiation portal monitors flagged a container full of faintly radioactive sneakers. The shoes were intercepted and never made it to the market. In this article, ANVS inspector Judith van Leeuwen and RIVM researcher Dannis 't Hart talk about the discovery, the Netherlands' strict rules for consumer goods and the international search for the source of the contamination.
Limits to radioactivity
The Netherlands has strict limits on radioactivity in the living environment. That includes limit values for radioactivity in materials and consumer goods. Radiation portal monitors are set up at Customs to check the radioactivity levels of goods from abroad. If they exceed the limit values, we intervene to prevent the goods from being sold on the market. In this way, we protect people and the environment from harmful radiation.
ANVS inspector Judith van Leeuwen is a Radiation Duty Officer (Dienstdoend Ambtenaar Straling, DDA), part of a response team for potential radiation incidents. "It's not unheard of for goods from abroad to exceed the limit values. What happened on 23 July 2025 was a remarkable case, though."
ANVS Radiation Duty Officer at Dutch Customs
Caesium-contaminated sneakers intercepted
Van Leeuwen: "Customs' portal monitor detected a shipping container emitting low levels of radiation. They confirmed the reading using handheld scanners. I received the notification within the hour. Meanwhile they had also reviewed the load manifest; a shipment of sneakers from Indonesia, destined for Switzerland."
Van Leeuwen and one of her colleagues inspected the container in a special Customs building. "The signal clearly indicated the presence of caesium-137. This radioactive substance is an artificial creation; it did not exist in nature originally. Caesium-137 is used in industry. It was also released during the Chernobyl nuclear disaster. You don't expect it in sneakers, though, so where was the contamination coming from?" The team took several shoes to the National Institute for Public Health and the Environment (RIVM) for further analysis.
Image: © RIVM
Scanning a shoe component with a handheld radiation detector
Lab research confirms contamination
Dannis 't Hart works at RIVM's radionuclides laboratory, where he often researches radioactive materials for the ANVS. Judith van Leeuwen gave him two shoeboxes to measure. "Most of the radioactive substances we find are naturally occurring radioactive materials, or NORM. That makes this contamination even more unexpected, as caesium-137 is an artificial substance. It has nothing to do with footwear manufacturing."
"After a few minutes of measurement, our gamma spectroscope was already detecting emissions typical of caesium-137," says 't Hart. "We continued our investigations: which specific parts of the shoes were affected? It was quite a puzzle. We carefully took the shoes apart. They were mostly clean; it was mainly the soles that were contaminated."
Image: © RIVM
Samples from the shoes
Disposal and international reporting
The caesium contamination proved to exceed Dutch standards for limit values. The maximum acceptable amount of radioactivity is 0.1 becquerel per gram of material. The sneakers' activity was as high as 1.3 becquerel per gram. The standard is a strict one; if you were to leave these shoes under your bed for two years, you would be exposed to the same amount of radiation as from one dental X-ray.
Judith van Leeuwen: "That's a similar dose to what you'd already be exposed to in a single day due to naturally occurring sources in your living environment such as substances in the soil, or cosmic radiation. Not a big health threat, in other words, but still, shoes shouldn't contain radioactive caesium." The owner of the sneakers was told they would need to be disposed of safely. For example, they could be sent to the Netherlands' Central Organisation For Radioactive Waste (COVRA) in Zeeland.
It took a while before that could happen, though, says Judith. "First, we needed to investigate which parts were and weren't contaminated. We are also still exploring the most suitable processing method." The long processing times can make such cases a challenge. "Detection isn't enough; it is followed by many conversations with the carrier, the manufacturer and the receiver to determine what action is required and by whom." Meanwhile, the shoes remain safely in storage. They were never available for sale.
Detection gate for ionising radiation at Dutch customs
International hunt for source of contamination
The ANVS announced the contaminated sneakers' detection on European and international networks for radiation incidents. The Netherlands leads the way in such announcements, says Van Leeuwen. Our country doesn't just announce large-scale incidents, but also much smaller ones such as the traces of radiation found in these sneakers. That promotes international awareness of radiation protection for consumer goods.
After the Netherlands' announcement, more cases of contamination were revealed. In August 2025 the United States found caesium-137 in a shipment of frozen shrimp; again from Indonesia. The Dutch announcement inspired BAPETEN, Indonesia's Nuclear Energy Regulatory Agency, to launch investigations of its own into the contamination source.
Contaminated industrial estate cleaned up
Experts at BAPETEN traced the caesium contamination back to an Indonesian industrial estate, approximately 70 kilometres to the west of Jakarta. Multiple businesses are located on the estate. Eleven radioactive caesium hotspots were detected. BAPETEN therefore carried out extensive clean-up activities.
RIVM researcher Dannis 't Hart: "Even if the dose was ultimately rather low, caesium-137 doesn't belong in consumer goods. Our detection and measurements made up a few small cogs of the machinery used to trace and clean up the contamination. It's quite special to have seen that whole chain in action."
In April 2026, the Indonesian nuclear and radiation protection regulator BAPETEN reported that its clean-up activities at the industrial site had been completed. The 11 hot spots included the shrimp and shoe factories, but also other locations on-site. All have been pronounced "clean and clear". The contamination is thought to have originated in a metal smelter on the site. Some 1136 tons of material were removed.
Protecting people and the environment at scrap yards
Caesium-137 is used in industrial applications as a source of gamma rays. Gamma rays may be used to measure liquids in closed tanks, for instance. Such radiation sources require authorisation. They also have to be disposed of safely after use.
Occasionally a radiation source ends up at a normal scrap yard by accident. Scrap dealers in the Netherlands use radiation portal monitors to check for these 'orphan' sources. If such a source becomes damaged, it could result in the release of radioactive materials. This spring, the ANVS began an audit of scrap yards. Such inspections help prevent the unchecked spread of radioactive substances in waste streams. Through our oversight, we improve the protection of people and the environment.